1. Field of the Invention
The present invention relates to a heat exchanger that is employed in an air conditioning system for vehicles and the like and constitutes a portion of the cooling cycle.
2. Description of the Related Art
A prior art heat exchanger, which is disclosed in Japanese Unexamined Patent Publication No. H7-190661, is constituted of tubes formed through extrusion molding and fins provided between the tubes and a pair of headers. This heat exchanger is employed as an evaporator or as a dual purpose type heat exchanger that can be switched so as to function as an evaporator or a condenser. Also, in order to efficiently discharge condensation adhering to the surfaces of the tubes when employed as an evaporator, an indented drain portion is formed on the surface of each tube. In addition, the drain portions are not formed at the ends of the tubes to ensure that the tubes can be easily inserted into the headers. While it is desirable to form the tubes with a small thickness in order to improve their heat communicating performance, there is a likelihood that the pressure withstand performance will be reduced if the tubes are formed too thin. To deal with this, a plurality of partitioning walls are formed inside the tubes to improve the pressure withstand performance of the tubes.
However, in recent years, in order to achieve an improvement in the productivity and a reduction in production costs, tubes are often formed using brazing sheet instead of forming the tubes through extrusion molding. As a result, in order to improve the pressure withstand performance of the tubes that are formed in a flattened pipe shape with brazing sheet, inner fins are inserted and brazed within the tubes.